The group was created in the wake of the 2014 Scottish independence referendum, in which 55 per cent of those who voted chose to keep Scotland within the UK.

[6] In 2021, three political academics carried out a study which demonstrated a statistically significant difference between the Remain / Leave format and the 2014 Yes / No question formulation.

[16] In addition, SIU's Chief Executive, Pamela Nash, has written articles to highlight the benefits to Scottish public spending which come from sharing across the UK.

[23] SIU also launched a 'End The Spend' petition calling on the SNP government to stop wasting taxpayer money trying to break up the UK.

[24] SIU's first campaign was to encourage tactical voting against the Scottish National Party during the 2015 UK general election.

[26] In the run up to the 2021 Scottish Parliament election, SIU launched its tactical voting campaign for voters whose priority was stopping an SNP majority and another referendum.

An SNP majority was stopped, with Sir John Curtice commenting that tactical voting probably played a part in this outcome.

[27] According to a Scottish Election Study by academics across the UK, released in May 2022, "significant numbers of people voted for both the Conservatives and Labour as part of efforts to defeat the SNP and strengthen the Union".

These have mostly used data obtained via Freedom of Information (Scotland) Act 2002 requests, and have included items covering health and income inequalities[30][31] and cancer waiting times.

[32] In January 2023, SIU released polling (conducted in December 2022), showing that most people in Scotland thought that the SNP is performing poorly in its handling of key public services.

[39] At various events, across the UK and online, SIU has been joined and supported by politicians from across the main pro-UK parties including Ruth Davidson,[40] Anas Sarwar, Christine Jardine,[41] David Mundell,[42] Andrew Bowie, Mike Rumbles,[43] Martin Whitfield, Beatrice Wishart, Jackie Baillie,[44] Murdo Fraser, Alistair Carmichael, Johann Lamont,[45] Ian Murray,[39] Alex Cole-Hamilton,[46] Willie Rennie,[47] Wendy Chamberlain, Jamie Stone, Michael Shanks,[48] Meghan Gallacher[49] Donald Cameron,[50] Blair McDougall,[51] Jackson Carlaw,[52] and Susan Murray.

[55] In 2016, Scottish National Party MP Natalie McGarry apologised and paid compensation, after sending a tweet about the leadership of SIU.